1. Field of the Invention
The present invention relates generally to a seal structure for a rotary body, such as a rotary shaft. The invention also relates to a vane-type rotary compressor having a compressor housing and a rotary shaft, between which a seal structure according to the present invention is interposed for establishing liquid-tight and gas-tight seal therebetween.
2. Description of the Background Art
The Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 61-169288 which has been assigned to the common assignee to the present invention, discloses a seal structure for a rotary body to be employed in the vane-type rotary compressor. The seal used in the illustrated arrangement includes a seal lip section and a seal ring. The latter mentioned element includes an annular washer-like backplate member and an elastometric seal ring member which is connected to the annular washer-like member by an annular band. This band is folded over an crimped to secure the two major sections, i.e. the seal lip section and the seal ring member, together.
The seal lip section is disposed on the inboard side of the seal ring in such manner that a portion thereof seats on the inner surface of the portion of the elastometric member which is in contact with the outer periphery of a rotary drive shaft. Upon being heated the crimped metal band and annular washer-like backplate member expand to the point where the elastometric member, which is subject to torque due to its sliding engagement with the drive shaft, begins to rotate with respect to the two metal elements, i.e. the washer-like member and the crimped metal band. This induces friction and associated wear which tends to shorten the life of the seal lip and seal ring.
In order to overcome the foregoing defect in the prior art, Australian Patent Application 77414/87 which corresponds to Japanese Utility Model First (unexamined) Publication No. 62-138958 and has been assigned to the common assignee to the present invention, discloses a seal structure which is not influenced by thermal expansion of the backplate and/or change of the seal ring in restricting rotation of the seal ring with the rotary body. For this end, the seal structure for a rotary body comprises an elastometric seal member disposed between a rotary body and a stationary member for sealing contact with the periphery of the rotary body for establishing a liquid-tight and gas-tight seal, the seal member having a first section to be mounted on the stationary member and a second section sealingly contacting the periphery of the rotary body, a flat metal member having a plane mating with the first section of the seal member, a holder member firmly seated on the stationary member and holding the first section and the flat metal member in an assembled form, and means for restricting movement of the seal member relative to the holder member in circumferential direction. The restricting means is incorporated with one of the flat metal member and the holder member and defines a space for accomodating bulging of the seal member due to elastic deformation thereof.
The prior proposed construction is successful in avoiding influence of expansion and/or change. However, a difficulty is encountered in the prior proposed arrangement in assemblying the seal structure to the rotary machine construction. Namely, as discussed earlier, the prior proposed invention comprises two separated seal members to establish liquid tight seal between a rotary body, such as a rotary shaft. One seal member is coupled with the metallic holder member and formed into a pre-assembly in installation and the other seal member is coupled with a core by insert molded manner as a pre-assembly. In the practical installation, the pre-assembly including the one seal member and the holder is at first forced into a rotary shaft receptacle bore so as to establish a seal therebetween. Thereafter, the secondary pre-assembly including the other seal member and the core, is forced into the rotary shaft receptacle bore for establishing the seal. Both of the pre-assemblies are of equal inner and outer diameters in order to be disposed between a uniform diameter of bore and the rotary shaft. The one seal member is made of a material for establishing liquid tight seal and also having low friction for reducing resistance against rotation of the rotary shaft. In the prior example, the metallic holder member coupled with the one seal member is maintained in contact with the inner periphery of the bore to establish liquid and the one seal is made of a material suitable for establishing liquid tight seal and low friction engagement with the rotary shaft.
In the practical installation to force the first installed pre-assembly, the metallic holder member contacts with the inner periphery of the bore to cause scratching on the inner periphery of the bore. The scratches formed in the inner periphery of the bore forms small gaps between the other seal member for causing leakage of the working fluid and affects for sealing ability of seal structure.